/*
 * Copyright (c) 2010, Andrea Palloni
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * - Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * - Neither the name of the copyright holder nor the names of its contributors may be used
 * 	  to endorse or promote products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package net.palla.biblio.server.dao;

import javax.jdo.PersistenceManager;

import net.palla.biblio.server.PersistenceUtils;

import com.google.appengine.api.datastore.Key;

public abstract class BaseDao {

	/**
	 * deletes an object
	 * @param o
	 * @throws Exception
	 */
	public void delete(Object o) throws Exception {
		PersistenceManager pm = PersistenceUtils.get().getPersistenceManager();
        try {
    		pm.currentTransaction().begin();
    		doBeforeDelete(pm, o);
            pm.deletePersistent(o);
            doAfterDelete(pm, o);
            pm.currentTransaction().commit();
        } catch (Exception e) {
			pm.currentTransaction().rollback();
			throw e;
        } finally {        	
            pm.close();
        }
	}

	/**
	 * This method is fired after a delete is successful
	 * @param o
	 * @return
	 * @throws Exception 
	 */
	protected abstract void doAfterDelete(PersistenceManager pm, Object o) throws Exception;

	/**
	 * This method is fired after post is successful.
	 * It contains both images before and after post.
	 * @param old the oject before it has been persisted
	 * @param n the object after it has been persisted
	 * @return the final object
	 * @throws Exception
	 */
	protected abstract Object doAfterPost(PersistenceManager pm, Object old, Object n) throws Exception;
	
	/**
	 * This method validates delete
	 * @param o
	 * @return
	 * @throws Exception 
	 */
	protected abstract void doBeforeDelete(PersistenceManager pm, Object o) throws Exception;
	
	/**
	 * This method validates or prepares data in child daos.
	 * Useful to calculate, for example, primary key
	 * TODO: better replace whit an AOP action
	 * @param o
	 * @return
	 * @throws Exception 
	 */
	protected abstract Object doBeforePost(PersistenceManager pm, Object o) throws Exception;
	
	/**
	 * Gets an object by Key
	 * @param id
	 * @return
	 * @throws Exception
	 */
	public Object getById(Key id) throws Exception {
		PersistenceManager pm = PersistenceUtils.get().getPersistenceManager();
		Object o = null;
        try {
        	pm.currentTransaction().begin();
            o = pm.getObjectById(id);
            pm.currentTransaction().commit();
        } catch (Exception e) {
			pm.currentTransaction().rollback();
			throw e;
        } finally {
            pm.close();
        }
        return o;
	}
	
	/**
	 * Saves or update data
	 * @param o
	 * @return
	 * @throws Exception 
	 */
	public Object saveOrUpdate(Object o) throws Exception {
		PersistenceManager pm = PersistenceUtils.get().getPersistenceManager();
        try {
        	pm.currentTransaction().begin();
    		Object old = doBeforePost(pm, o);
            Object n = pm.makePersistent(old);
            n = doAfterPost(pm, old, n);
            pm.currentTransaction().commit();
            return n;
        } catch (Exception e) {
			pm.currentTransaction().rollback();
			throw e;
        } finally {
            pm.close();
        }
	}
}
